Department of Mathematics, Swinburne University of Technology, P.O. Box 218, Hawthorn, Victoria 3122, Australia.
J Chem Phys. 2019 Oct 28;151(16):164102. doi: 10.1063/1.5124715.
We have computed the two- and three-particle contribution to the entropy of a Weeks-Chandler-Andersen fluid via molecular dynamics simulations. The three-particle correlation function and entropy were computed with a new method which simplified the calculation. Results are qualitatively similar to Lennard-Jones systems. We observed a numerical instability in the three-particle contribution. This phenomenon has been previously detected when the traditional method is used; thus, it is likely to be intrinsic in the computation. While the effect of statistical fluctuations can be removed through an extrapolation procedure, the discretization error due to the finite bin size is more difficult to characterize. With a correct choice of the bin size, a good estimate of the three-particle entropy contribution can be achieved at any state, even close to the freezing point. We observed that, despite the fact that the magnitude of the three-particle contribution increases significantly compared to that of the two-particle contribution as freezing is approached, the error induced from overestimation of the excess entropy by the two- and three-body terms exceeds that induced by approximating the excess entropy with the two body term alone.
我们通过分子动力学模拟计算了 Weeks-Chandler-Andersen 流体的两体和三体对熵的贡献。三体相关函数和熵是通过一种简化计算的新方法计算的。结果与 Lennard-Jones 体系定性相似。我们观察到三体贡献中的数值不稳定性。当使用传统方法时，已经检测到这种现象；因此，它可能是计算中的固有现象。虽然可以通过外推程序去除统计波动的影响，但由于有限的-bin 大小导致的离散化误差更难描述。通过正确选择-bin 大小，可以在任何状态下（即使接近冰点）实现三体熵贡献的良好估计。我们观察到，尽管随着接近冰点，三体贡献的大小与两体贡献相比显著增加，但通过两体和三体项过高估计过剩熵引起的误差超过了仅用两体项近似过剩熵引起的误差。
